1. Field of the Invention
The present invention is directed to stabilized cable filler compositions for cable and wire.
2. Description of Related Art
For certain uses, cable and wire are surrounded by an insulation layer, which, in turn, is surrounded by filler compositions that, in turn, are surrounded by jacket compositions. Such filler compositions, when employed, should possess physical properties that are desirable for the given use.
A typical telephone cable is constructed of twisted pairs of metal conductors for signal transmission. Each conductor is insulated with a polymeric material. The desired number of transmission pairs is assembled into a circular cable core, which is protected by a cable sheath incorporating metal foil and/or armor in combination with a polymeric jacketing material. The sheathing protects the transmission core against mechanical and, to some extent, environmental damage.
Telecommunication cable, whether of the metallic or fiber optic variety, is frequently employed where water, as a result of jacket deterioration, can pass through openings in the jacket and thereafter migrate through the filler component to the insulation layer of the cable system.
However, water entry into either metal conductor or fiber optic cables may be undesirable for several reasons. For example, such water entry may lead to deterioration of cable transmission properties owing to corrosion, particularly where cable end portions are spliced together. In order to protect such cables, it has become common practice to encase certain of their segments in an enclosure that acts as an extension of the cable sheath or cover. It has also become common practice to encapsulate the enclosed cable segment with a curable encapsulant in order to prevent water immigration. Sealants for this purpose are disclosed in U.S. Pat. No. 4,221,696.
Grease-filled telephone cables were developed in order to minimize the risk of water penetration, which can severely upset electrical signal transmission quality. Here, a hydrocarbon filler grease is used to provide a watertight cable by filling the air spaces in the cable interstices. Although the cable filler grease will extract a portion of the antioxidants from the insulation and/or jacket layers, the watertight cable will not exhibit premature oxidative failure as long as the cable maintains its integrity.
In the cable transmission network, however, junctions of two or more watertight cables are required and this joining is often accomplished in an outdoor enclosure known as a pedestal (an interconnection box). Inside the pedestal, the cable sheathing is removed, the cable filler grease is wiped off, and the transmission wires are interconnected. At this point, the pedestal now has exposed insulated wires that are often subjected to high temperatures, air, and/or moisture. This environment, combined with the reduction in antioxidant levels in the insulation and jacket layers brought about by extraction into the filler layer, can cause the insulation in the pedestal to exhibit premature oxidative failure. This failure can then cause embrittlement of the insulation and jacket layers, making them prone to cracking and flaking, which can cause a loss of electrical transmission performance.
High levels of antioxidants could be used in the polymeric insulation and jacket layers, but this would alter the performance characteristics of the insulation and would be undesirable economically owing to the cost of the antioxidants. Thus, there is a need for antioxidants capable of resisting extraction by the filler layer to the extent necessary to prevent oxidative failure and help ensure a 30 to 40 year service life.
U.S. Pat. No. 3,255,136 discloses stabilizer compositions said to be useful in the stabilization of polypropylene against degradative deterioration in physical properties as a result of exposure to light and air, particularly at elevated temperatures, and over long periods of time. The stabilizer system comprises three stabilizers, namely, an organic mono- or polyhydric phenol, an organic phosphite, and a thiodipropionic acid ester. According to the patent, this stabilizer system not only improves the resistance of the polymer to discoloration and embrittlement upon exposure to air and light at normal atmospheric and elevated temperatures, particularly over long periods of time, but also improves the resistance of the polymer to reduction in melt viscosity when worked at elevated temperatures in the presence of oxygen.
U.S. Pat. No. 4,190,570 discloses a waterproof filling and flooding composition for communication cables that comprises 90 percent or more by weight of petrolatum, about 5 to 7 percent polybutene-1, 0.5 to 2.0 percent polyethylene, and the remainder an amorphous saturated rubber, such as ethylenepropylene rubber (EPR), which is said to exhibit flow resistance at temperatures of 160.degree. to 170.degree. F. and even higher.
EP 0 675 508 B1 discloses a grease-filled cable construction that contains an antioxidant that is said to resist extraction so that it can be maintained in cable insulation at a satisfactory stabilizing level. The disclosure of this publication is hereby incorporated herein by reference.
In the wire and cable industry, extended thermoplastic rubber (ETPR) and petroleum jelly/polyethylene are often incorporated into the filler component to effect water protection of the insulation layer. Examples of cable segments that are often placed in enclosures and thereafter encapsulated include:
(1) the regions where two or more cables are spliced together; PA1 (2) the ends, or end block portions, of the cable; and PA1 (3) the junctions between air-pressurized cable and hydrocarbon grease-filled cable, or pressure block. PA1 is (a) metal dithiocarbamate salts, PA1 (b) amine antioxidants, and PA1 (c) sterically hindered phenolic antioxidants, PA1 R.sub.2 and R.sub.3 are independently selected from the group consisting of methyl, phenyl, and p-tolyl radicals; PA1 R.sub.4 is selected from the group consisting of methyl, phenyl, p-tolyl, and neopentyl radicals; PA1 R.sub.5 is selected from the group consisting of methyl, phenyl, p-tolyl, and 2-phenylisobutyl radicals; and, PA1 R.sub.6 is a methyl radical. ##STR4## wherein R.sub.1 through R.sub.5 are independently selected from the radicals shown in Formula I and R.sub.7 is selected from the group consisting of methyl, phenyl, and p-tolyl radicals; PA1 X is a radical selected from the group consisting of methyl, ethyl, C.sub.3 -C.sub.10 sec-alkyl, .alpha.,.alpha.-dimethylbenzyl, .alpha.-methylbenzyl, chlorine, bromine, carboxyl, and metal salts of the carboxylic acids where the metal is selected from the group consisting of zinc, cadmium, nickel, lead, tin, magnesium, and copper; and, PA1 Y is a radical selected from the group consisting of hydrogen, methyl, ethyl, C.sub.3 -C.sub.10 sec-alkyl, chlorine, and bromine. ##STR5## wherein R.sub.1 is selected from the group consisting of phenyl or p-tolyl radicals; PA1 R.sub.2 and R.sub.3 are independently selected from the group consisting of methyl, phenyl, and p-tolyl radicals; PA1 R.sub.4 is a radical selected from the group consisting of hydrogen, C.sub.3 -C.sub.10 primary, secondary, and tertiary alkyl, and C.sub.3 -C.sub.10 alkoxyl, which may be straight chain or branched; and PA1 X and Y are radicals selected from the group consisting hydrogen, methyl, ethyl, C.sub.3 -C.sub.10 sec-alkyl, chlorine, and bromine. ##STR6## wherein R.sub.9 is a radical selected from the group consisting of methyl, phenyl, and p-tolyl; PA1 R.sub.10 is a radical selected from the group consisting of methyl, phenyl, p-tolyl and 2-phenyl isobutyl; and PA1 R.sub.13 is a radical selected from the group consisting of methyl, phenyl, and p-tolyl; PA1 R.sub.14 is a radical selected from the group consisting of methyl, phenyl, p-tolyl, and 2-phenylisobutyl; and PA1 R.sub.15 is a radical selected from the group consisting of hydrogen, .alpha.,.alpha.-dimethylbenzyl, .alpha.-methylbenzhydryl, triphenylmethyl, and .alpha.,.alpha.-p-trimethylbenzyl.
One problem that arises, occurring when an antioxidant ingredient of the insulation or jacket layers is extracted from the insulation or jacket layers and incorporated into the filler, is that the wire and cable product is left unsuitable for its intended purpose, principally because of deterioration of the jacket and/or insulation layers.
In general, to stabilize the filler component of cable and wire, at least one antioxidant ingredient is conventionally incorporated into the filler composition. Similarly, to stabilize the insulation and jacket components, at least one other antioxidant, usually different from the filler antioxidant, is incorporated into the jacket composition.
In this regard, conventional stabilizers for polyolefin-based filler components of commercial cable and wire systems include organic phosphites, which may be combined with such polyhydric phenols as BHT and BHA, as are disclosed in U.S. Patent 4,190,570, supra.
One aspect or feature of the present invention involves waterproof, high-performance, cost-efficient stabilizer systems for filler components of conventional wire and cable systems, a result of this invention.
Such waterproof compositions may, indeed, be deemed indispensable in protecting those communication cables that are manufactured mainly from hydrocarbon materials.